1. Field of the Invention
The present invention relates to a homeotropic alignment type liquid crystal display device which performs transmissive display and reflective display.
2. Description of the Related Art
A homeotropic alignment type active matrix liquid crystal display device has been known. This liquid crystal display device comprises a pair of substrates facing each other with a predetermined gap therebetween, and a liquid crystal layer having negative dielectric anisotropy, which is sealed between the pair of substrates. Of the facing internal surfaces of the pair of substrates, the internal surface of one substrate has thereon, a plurality of pixel electrodes arranged in a row direction and in a column direction in a matrix, a plurality of thin film transistors (hereinafter referred to as TFT) provided correspondingly to the plurality of pixel electrodes respectively and connected to the corresponding pixel electrodes, and a plurality of gate lines and data lines formed between the rows of pixel electrodes and between the columns of pixel electrodes for supplying a gate signal and a data signal to the pixel electrodes in the corresponding rows and corresponding columns. An opposing electrode, which faces each of the plurality of pixel electrodes, is formed on the internal surface of the other substrate of the pair of substrates. Further, a homeotropic alignment film is formed on the internal surface of each of the pair of substrates so as to cover the above-described electrode(s).
This homeotropic alignment liquid crystal display device has its pixels defined by the regions where the plurality of pixel electrodes and the opposing electrode face each other, and displays an image by controlling the alignment of the liquid crystal molecules by applying a voltage across the facing electrodes in each of the plurality of pixels. In this case, by the application of the voltage, the liquid crystal molecules of each pixel are aligned to lie down toward the substrate surface from the homeotropically aligned state.
In such a homeotropic alignment liquid crystal display device, the direction in which the liquid crystal molecules are aligned and lie down in response to the voltage applied, is not uniform throughout the pixels. Therefore, the alignment state of the liquid crystal molecules varies from pixel to pixel, producing display unevenness.
Hence, such a liquid crystal display device is proposed, whose pixels each have a plurality of domains with different directions in which the liquid crystal molecules are aligned, in order to stabilize the alignment state of each pixel and to have a wide view angle characteristic.
For example, as described in the publication of the U.S. Pat. No. 2,565,639, such a homeotropic alignment liquid crystal display device has X-shaped openings formed in the opposing electrode, so that when a voltage is applied across the two facing electrodes, the liquid crystal molecules in each pixel may be aligned to lie down in four directions toward the center of the X-shaped opening.
However, this liquid crystal display device is a device for transmissive display and cannot perform reflective display. Further, the X-shaped opening needs to be formed to have a sufficiently large width, since it is necessary to make each pixel have domains whose alignment directions are different from each other due to the X-shaped opening formed in the pixel, and this requires the respective domains not to interfere with each other. Accordingly, in each pixel, the area of the opening, which cannot be controlled by an electric field, is increased to thereby reduce the area over which the electrodes face each other, raising a problem that the aperture ratio is reduced.